1. Field of the Invention
The present invention relates to parachutes, and more particularly, to the gliding parachute of the ram-air type.
2. Description of the Prior Art
The early parachutes were dome-like in shape and were constructed by sewing a plurality of panels together to define a hemispherical structure when inflated. These dome-like parachutes incorporated slits, vents or baffles in the panels for controlling the flow of air therethrough, both to facilitate deployment and to provide maneuverability. These early parachutes were adapted primarily for nearly vertical descent and generally did not permit a load or jumper to be carried over substantial horizontal distances to a landing area.
A typical gliding parachute comprises upper and lower panels, generally rectangular in shape, separated by airfoil shaped ribs defining a plurality of open cells between the upper and lower panels. In flight, air is introduced into each cell by the ram air principle and the gliding parachute assumes a wing-like configuration.
The gliding parachute is fabricated of a low porosity nylon cloth and can be packed and deployed in a manner similar to a conventional dome-like parachute. Suspension lines are attached to the lower panel of the gliding parachute to hold the jumper or load and are distributed along the lower panel in such a manner so as to distribute the aerodynamic forces over the parachute.
The history of the gliding parachute, known in the art as a para-foil, which denotes the combination of parachute and airfoil, can be traced back to U.S. Pat. No. 2,546,078 to G. S. Rogallo, et al which disclosed a flexible kite, of flexible, non-rigid material with wing-like sections extending transversely on either side of the center line of the kite. The modern para-foil is based on this unique kite design.
U.S. Pat. No. 3,131,894 to D. C. Jalbert discloses one of the first multi-cell gliding parachutes, having a substantially triangulated or wedge shaped canopy top which assumed a flattened or slightly dished form in flight. The under or concave lower side of the canopy top and an attached peripheral skirt formed a construction that was interiorly divided by crossed partition strips forming a plurality of cells. Vertical dividing panels were attached to the upper end of some of the partition strips forming air channels opened at the rear of the canopy, constituting outlets for the air flowing upward through the cells. Movable flaps or other air controlling means were provided at the outlets for steering control.
U.S. Pat. No. 3,285,546 also to D. C. Jalbert appears to be the first conventional multi-cell wing type parachute incorporating the true shape of an airfoil. The Jalbert 546 patent discloses a gliding airfoil-shaped parachute comprising an upper canopy and a bottom planar skin connected together by a plurality of vertically extending spaced apart ribs which define longitudinal channels through which air flows to sustain a conventional airfoil shape. The inflated parachute has a downwardly facing intake opening along its leading edge and a restricted outlet opening along its trailing edge. Connected to the bottom skin of the parachute are a plurality of fabric wedges which provide for even distribution of the forces of the suspension lines to the bottom skin to permit the bottom skin to retain a flat configuration during flight.
U.S. Pat. No. 3,428,277 to W. J. Everett, Jr. discloses a gliding parachute including a plurality of inflatable ram-air scoops along the leading edge of the wing which serve to maintain the leading edge extended to prevent buckling or inwardly folding thereof.
U.S. Pat. No. 3,524,613 to J. D. Rueter, et al discloses a multi-cell ram-air gliding parachute in which the suspension lines were connected and arranged so as to give the wing a predetermined contour. The arcuate shape is supposedly utilized to prevent buckling of the central portion of the parachute during flight. The vertical dividers between the upper and lower panels of the wing are provided with openings that permit lateral airflow to equalize air pressure within adjacent channels.
U.S. Pat. No. 3,724,789 of Snyder discloses a gliding ram air parachute of the multi-channel type in which the suspension lines are secured to the airfoil-shaped ribs between the upper and lower panels of the wing with a plurality of reinforcing tapes to distribute the load and maintain the airfoil shape of the inflated parachute.
U.S. Pat. No. 3,822,844 to Sutton discloses a gliding parachute of the ram-air type wherein there is a plurality of openings in the top and bottom wall of each cell, which is supposed to improve the stability of the parachute, especially under conditions of vertical descent.
U.S. Pat. No. 3,866,862 to Snyder discloses attitude and braking controls for ram-air type parachutes.
U.S. Pat. No. 3,972,495 again to Jalbert discloses a ram air parachute having upper and lower flexible layers with a leading edge and a trailing edge, a wall of the wing having an opening facing outward from the bottom or a side of the wing, forming an inlet for flow of pressurized air into the wing, and a normally opened flexible valve for the opening closable by the air pressure to seal the opening when pressurized air is admitted to the wing.
U.S. Pat. No. 4,015,801 to Womble, et al discloses a maneuverable ram-air inflated flexible aerial parachute incorporating a plurality of forward facing air cells having their first openings along the leading edge thereof and including rearward facing second openings on top of the parachute so as to displace the separation point of the relative airflow across the upper surface further toward the trailing edge to produce a higher lift. U.S. Pat. No. 4,191,349 to Pravaz discloses the basic para-foil incorporating the velocity slots of Womble and further including a flap-type arrangement on the trailing edge to increase the lift of the para-foil by creating a hyperlift effect near the trailing edge.
U.S. Pat. No. 4,389,031 to Whittington discloses a flat ram-air parachute incorporating a single cell parachute with an upwardly extending central recess defining an exit at the trailing edge of the parachute to provide stable forward drive.
U.S. Pat. No. 4,399,969 to Gargano discloses a gliding parachute of the flexible, multi-cell airfoil type having a length to width ratio in the range approximately 2:1 to 2.85:1, a maximum camber height to chord ratio in the range of approximately 0.1:1 to 0.2:1, a wingspan to load attachment distance ratio of approximately 2:1, an attachment point approximately 25% to 45% of the chord aft of the leading edge. A special pilot chute and bridle assembly is incorporated so that upon deployment of the main chute, the pilot chute will automatically collapse to substantially reduce its drag, thereby improving the glide ratio of the main parachute.
As noted in the prior art, gliding parachutes have been made with multiple cells for channeling the flow of air in a generally horizontal direction through the parachute to sustain the desired airfoil shape. Much emphasis has been placed on the fabric and rigging configurations of previous gliding parachutes in an effort to approximate, as close as possible, a conventional airfoil shape.
Whatever the form of the fabric portion in rigging previously employed in a gliding parachute, there has always been a tendency for the shape of the inflated wing to depart from the desired conventional airfoil shape thereby destroying the general aerodynamic flow pattern and flow characteristics through and around the inflated wing thereby reducing the glide ratio. For example, the leading edge of the wing frequently buckles or folds inwardly under the pressure of air exerted on it as the parachute travels forwardly. Furthermore, the lower surface of the wing does not remain flat or retain its airfoil shape with very little camber. Further, all prior art para-foils employ two cells between suspension lines and large ram-air openings for the cells. This causes the top surface of the para-foil to become bulbous and thereby destroys the optimum airfoil shape. Further, the large ram-air openings cause leading edge turbulence which further destroys lift on the upper surface.
Consequently, a need exists for improvements in gliding parachutes which will maintain the airfoil shape of the gliding parachute while in flight and further improve the glide ratio and aerodynamic characteristics by increasing upper surface lift, lowering leading edge turbulence, reducing drag, and helping to prevent collapse in stall conditions.